Method of making dies



April 1 E. H. PORTER ET AL 7 2,466,272

METHOD OF MAKING DIES Filed April 23, 1945 Q///J il/w INVENTORS ELBEQT H. POIQ'TEQ FPED M. BUSHWAY 5 I BY I ATTORNEY Patented Apr. 5, 1949 METHOD F MAKING DIES ElbertHaPorter and Fred M. Bushway, ,San Diego, Calif., .assignors to Solar Aircraft Company, San Diego, Calif a corporation or California Application April 23, 1945, Serial No. 589,782 3' Claims. (01. 22-195) This invention relates to the die stampingart in which metal sheets are bent into desired shapes by pressing or striking, them between dies.

An object of the: invention is to simplify and reduce the cost of making dies for stamping sheet members.

'Anotherobjectisto reduce the skill required in making dies for sheet stamping.

A more specific object is to provide a simple and effective way of making. one die from its mating die.

Other and more specific objects and features of the invention will become apparent from the detailed description to. follow, which refers to the drawing.

In making some stampings, such as half stampings of semi-circular cross-section, it is customary to use a female die, commonly referred to as the "die and a cooperating male die which is most commonly referred to as the punch. Obviously the punch must be smaller than the die by an amount equal to the thickness of the stamp ing that is to be made in the die, but because of the fact that the punch closely approaches-the die in shape, many attempts have beenmadeto form the punch from the die as a mold. However, it is necessary to compensate for the thickness of the stamping that is to be produced; and this has introduced difliculties.

One method that has been employed wasto lay strips of wax in the die, the. strips extending transversely across the die, and being, spaced apart where the cross-section of the die changes longitudinally, after which the die'was'filled with plaster. After the plaster had set; it was removed from the die, and the raised portions, corresponding to the spaces betweenv the wax strips in the die were removed'by hand scraping.

Another method was to apply narrow strips of wax equal to the metal thickness along the edges of the die and fill the die with plaster. Thereafter, the main body of the plaster cast was scrapedby hand to attempt to reduce its radius throughout by an amount equal to the thickness of the wax. strips.

Neither ofthese methodshasbeen very satisfactory for the reason that they required con siderable hand work and considerable skill on the part of the worker.

In accordance with the present invention,. a plaster cast can be molded, in thedie, to the desired shape of the finished punch without scraping operations requiring special skill on the part of the operator. The invention is based on the principle'thatif the punch is lowered into contactwith the bottom of the die, it will contact the latter over'an area at the bottom of'the' dieand will be spaced from the die increasing distances toward the edges. Hence, by building up the side walls of the die with wax that diminishes in thickness toward the bottom. ofxthedie, a ,moldresults that closely" corresponds. to. the desired punch shape.

The practicability of I the invention depends upon our'furth'er discoveryofa simple and effec tlvemethodof building up-the side-walls ofv the die to the desired thickness. We do thisby first forming, two elongated strips of sheet Wax thatare wedge shape in cross section and; that taper. from a featherv edge on oneside to, an edge on the other side of thickness equal to the sheet metal-that is to be shaped by the die. These wedge shaped wax strips are thenpressed against the sides of the die with their thick edgesflus-h with the top of the die. Because of their flexible nature, the wax strips can be readily deformed to lie against the curved sides ot'the die.

The die built up with wax-as described is then filled with plaster,which, after it has set, is"removed from the die and used asa pattern to form the punch in accordance with wellaknown practice.

The improved method, as; outlined, involves only'routineoperationsthat-can be readily performe'dby an ordinaryworker and. no special skill is required such as was necessary in the processes involvlngrthe scraping of plaster casts.

Referringnow to the drawing:

Fig. 1 is across-section showing a punch and die with a shaped" metal work-piece therebetween;

Fig. 2 is a cross-sectionisimilar'to Fig. Lbut showing the work-pieceremoved' and thepunch and die brought fully together;

Fig. 3 isa cross-sectionillustrating-a method of making a wedgeshape. strip of wax;

Fig. 4 is a cross-sectionof a wedge shape piece of wax produced by the method of'Fig'. 3;. and Fig. 5 isaperspectiveviewof a die that has beenbuiltup with wax, in accordance withthe invention, preparatory to the casting of a plaster pattern. therein.

Referring first to Fig. 1, there'is disclosed-a die in and... punchll used for forming: a half stamping, aiormed halt'stamping I 2 being shown interposed between the die: and punch. The curvedv portion of the half I stamping I I! may be exactly semi-circular in arcuate extent, although not necessarily; It is shown of exaggerated-thickness in -Fi'g; 1 to moreclearly illustrate the prob, lems involved; It will be observedfrom Fig. 1 that if the work-.-

pieee- I2 is of uniform thickness: throughout; the

curved: portions of thedie and'punchare both of circular curvature, but the radius of'curvatu-re of: the punch isless-than that of theme by the thicknessof the-- workpiece; It follows that iithe work-piece is removed and the punch is fully lowered into the die, as illustrated in Fig. 2, the mid-portion of the punch will contact the midportion of the die, and likewise the shoulders 13 of the die will be contacted by the shoulders i of the punch- 'Howeven the upperedges ofthe In accordance with the pres'entinvention, we

build up the side wall portions of the die to approximate the shape of the punch bystick ing wedge shaped wax strips to the sides of the die,

these wax strips corresponding in shape approxi- 4 thickness and width of the spaces It and H in Fig. 2. The strips of Fig. 4 have a thickness varying linearly from the thin to theithlck edge, whereas thevariation in thickness of the spaces-i6 and I7 is not linear, and their width is greater than the width of the strips. However, it is found in practice that where the workpiece is from .016

mately to the spaces l6 and I1 between the punch and die in Fig. 2. v

- The wedge shaped wax strips may be prepared in various ways, but-a convenient and practical procedure will be explained with reference" to Figs. 3 and 4. Referring first to Fig. 3 a strip of wax i8, somewhat longer than the die, is laid on a flat surface I9 with one edge 20 of the wax strip overlapping one edge 2| of the surface i9, which may be determined by a table having a smooth hard top. The edge 20 of the wax is rolled slightly around the edge 2| to secure it firmly in place. A straight strip 22, of hard material such as steel is placed on top of thewax strip 3, with one edge 23 spaced from and parallel to the edge 2|. The spacing between the edge 2| of the surface I!) and the edge 23 of the strip 22 depends upon the radius of the die that is to be built up, and upon the thickness of the strip 22 relative to the thickness of the work sheet that is to be formed in the die. If the strip 22 is about the same thickness as the work sheet, the distance between the edges 2| and 23 should be about twice the radius of the die. The wax strip is then reduced to a triangular cross section by moving a straight edged scraper longitudinally along the wax strip, using the upper corner of the edge 23 and the upper corner of edge 2| as limiting guides for the scraper. The cutting edge of the scraper being straight, the scraped wax strip ha a beveled edge of a very small angle. The strip is then cut longitudinally to provide a strip that is Wedge-shape in crosssection as illustrated in Fig. 4, the width of this strip being approximately equal to the radius of the die.

Two wax strips as shown in Fig. 4 are formed and are placed in the die as shown in Fig. 5. The wax adheres to the wall of the die and is readily deformed to assume the curvature of'the die. Thereafter, the die is filled with plaster, which is allowed to set and is then removed from the die and used as a pattern to prepare the finished punch in accordance with well known foundry practice.

If the die is of uniform cross-section longitudinally, the wedge-shaped wax strips can be placed in the die intact. On the other hand, if the die has a curved upper surface, as illustrated in Fig. 5, it is desirable to make cuts or serrations' 25 in the thin edges of the-wax strips to allow the upper edge to conveniently follow the curve. Of course these cuts or serrations 25 produce ridges in the plaster cast, but the ridges are of such small area that they can be quickly and easily scraped down flush with the general surface of the cast.

The wax strips formed as described do not correspond exactly in thickness and width to the inches to .030 inches thick, it is satisfactory to make the wax strips of width equal to an arc of about 30 in the die. For workpieces of thickness between .030 and '.100, it is satisfactory to make the wax strips of width equal to an arc of about 60 in the die. Such strips, even though they vary in thickness in linear relation as shown in Fig. 4, produce punches that compare favorably in accuracy with the best punches that are producable by prior known methods and that can be made at a cost substantially less than the cost of pro ducing punches by the most satisfactory prior methods.

Although for the purpose of explainingthe invention, it has been described in detail with reference to a die for making a half stamping of semi-circular cross-section, its utility is not limited to dies of circular curvature, but is applicable generally to dies having relatively steep side walls and relatively flat bottoms.

We claim:

1. In the art of sheet stamping pieces of curved cross-section, the method of making a pattern for a complementary die from a first die of said curved cross-section comprising: preparing two strips of deformable material, each of width less than the depth of said first die and tapering laterally in thickness from the thickness of the work sheet to be stamped at one edge to a feather edge at the other edge, securing said strips against the opposite side walls of said first die with their thick edges flush with the edges of the die, and using said built up'first die as a mold for casting the pattern for the complementary die.

2. The method described in claim 1 in which said deformable material is wax.

3. In the art of sheet stamping, the method of making a pattern for a punch for use with a die of approximately semi-circular cross section, comprising: building up the side walls of the die by an amount that is uniform longitudinally but that tapers from the thickness of the sheet to be stamped at the edges of the die, to a feather edge at points intermediate said edges and the bottom of the die, and using said built-up die as a mold for casting the pattern for the punch.

ELBERT H. PORTER. FRED M. BUSHWAY.

REFERENCES CITED The following references are of record in the file of this patent:

tion, by F. D. Jones, published by The Industrial Press, New York, N. Y. (1941), pages 536. 537. 

